1. Field of the Invention
This invention generally relates to a television receiver, and more particularly to a correction circuit for side pincushion distortion of the raster in the television receiver.
2. Description of the Prior Art
It is known in the art that side pincushion distortion of the raster on a cathode ray tube in a television receiver may be substantially eliminated by modulating the horizontal deflection current with a parabolic signal at the vertical scanning rate. In one known arrangement; a saturable reactor is connected in series with a horizontal deflection coil in the television receiver. The impedance of the reactor is modulated by the vertical parabolic signal. In another known arrangement, the power supply voltage supplied to a horizontal deflection circuit in the television receiver is modulated with the vertical parabolic signal. Although these arrangements are capable of correcting outside pincushion distortion, they are unable to eliminate inside pincushion distortion. A side pincushion distortion correcting circuit is disclosed in U.S. Pat. No. 4,088,931 in which inside pincushion distortion can be corrected. In this circuit, a correcting coil is connected in series. with the horizontal deflection coil, and the series circuit of a capacitor and a controllable switch is connected in parallel with the correcting coil. The controllable switch is turned on during the latter half of the horizontal retrace period at a time which is modulated by the parabolic wave signal at the vertical rate. The impedance of the circuit connected in series to the horizontal deflection coil is thus modulated by the parabolic wave signal, and side pincushion distortion of the raster is eliminated. Further, the amount of the S-shape correction is also modulated by the parabolic wave signal, so that inside pincushion distortion is also eliminated.
Pincushion distortion in the prior art correction circuit described above varies with the brightness of the raster. Therefore proper correction of side pincushion distortion can not be achieved for a picture having varying brightness. Furthermore, since this variation occurs dynamically in response to the brightness of a picture being reproduced, the amount of correction of side pincushion distortion also varies dynamically. Such dynamic variation is very undesirable in the reproduced picture.